Anatomy and physiology of the rectum and anus.

Anorectal physiology is complex and involves the interaction of multiple mechanisms. Advances in physiological testing have led to a great deal of research, which has increased our knowledge of normal and disordered physiology, and modified our therapeutic approach. As a consequence, many concepts in anatomy have been revised. We have reviewed aspects of the anatomy and physiology of the rectum and anus together with the applications of the new concepts.